Differential assemblies are used in motor vehicles to allow the wheels to turn at different rotational speeds while still providing power to the wheels. Various types of differential assemblies are used to redirect the transfer of power to the driving axles.
In a standard open differential, as a vehicle turns, power is provided through a pinion and ring gear to the differential housing. As the inner and outer wheels trace paths of different radii, side gears attached to right and left axle half shafts are allowed to turn at different speeds by their interconnection through intermediate spider gears, which rotate with the housing.
As long as traction is maintained between the drive wheels and the road surface, the power is properly distributed to the wheels through the differential assembly. However, when traction is reduced or lost altogether at one or both wheels, a standard open differential assembly will cause one wheel to spin uselessly, providing little tractive power to the wheels. For instance, if one tire is on ice or some other slippery surface and the other tire is on dry pavement, slip will occur at the low friction side and the torque applied to the non-slipping tire will be limited to the torque generated at the slipping tire. In such circumstances, very little power will be delivered to the wheel on the dry pavement and the vehicle will not be powered forward or backward. Therefore, there is a need to lock the axle half shafts together in certain situations causing both wheels to spin at about the same speed, irrespective of differing coefficients of friction encountered by the drive wheels.
It is known in the art to selectively lock other drivetrain components using roller/ramp clutch assemblies. For example, the two-way over-running clutch assembly described in U.S. Pat. No. 5,927,456, and which is hereby incorporated by reference, describes a clutch assembly of a roller/ramp variety and the mechanism by which the rollers are retained and biased in the assembly. In addition, the rotation transmission device described in U.S. Pat. No. 5,924,510, also hereby incorporated by reference, discloses a device which includes a clutch assembly mounted in the transfer case of a four-wheel drive vehicle that can selectively transmit a driving torque.
Typically, these types of over-running clutches must include complex sensors to determine when the clutch is engaged and to send a signal to the operator of the vehicle indicating engagement status. Therefore, there is a need for an over-running clutch of the type described above that includes a simple, reliable lock indication device that will send a signal to the operator of the vehicle, or to the electronic control unit, indicating that the clutch is either engaged or disengaged.